We will study the mechanisms by which virulent and oncogenic viruses replicate, and how this replication affects host cells. In particular, cellular and viral protein metabolism (synthesis, post- translational modification and degradation) will be examined, with the aim of gaining insight into the processes of cell killing by virulent viruses and cell transformation by oncogenic viruses. For reasons of efficiency, convenience and ease of comparisons a single cell line, the murine plasmacytoma MOPC-460, will be used for all our experiments. This line has already proven very useful for studies in whole cells and in cell-free extracts, since it can be grown in either solid or ascitic form in mice as well as in tissue culture. Encephalomyocarditis virus (and double-stranded RNA therefrom) will be used in studies on the mechanism of cell killing in general, and the shut-off of cellular protein synthesis in particular. The relationship of the A-type particles produced by plasmacytoma cells to RNA tumor viruses will be investigated, and their putative role in transforming the cells will be examined. Comparative studies between murine plasmacytoma and human myeloma cells and A-type particles will also be conducted. Bibliographic references: "Identification of a Viral Protein Involved in Post-Translational Maturation of the Encephalomyocarditis Virus Capsid Precursor," by C. Lawrence and R.E. Thach, J. Virol. 15, 918-928 (1975). "Inhibition of Host Cell Protein Synthesis by Encephalomyocarditis Virus Infection," by F. Golini and R.E. Thach, INSERM Colloquium: In Vitro Transcription and Translation of Viral Genomes 47, 369-372 (1975).